During the past three decades, efforts have been made in the detergent industry to convert from the eutrophying polyphosphates to more environmentally acceptable materials such as polycarboxylic acid polymers (e.g., polyacrylic acids).
Polycarboxylic acid polymers have been known to impart favorable performance and processing properties when incorporated into detergent formulations. Polymers may act as builders or as builder-assists in these formulations. They prevent incrustation of hardness ions onto the fabric, and surfaces, and improve soil or stain removal and anti-redeposition properties of the detergents.
Because large volumes of chemicals are used in detergent applications, and because these chemicals may eventually enter the environment and reside in subsurface waters or open bodies of surface waters, it is highly desirable for such chemicals to be degradable.
While the polycarboxylic acid polymers and copolymers currently used in detergents and water treatment applications do not suffer from the drawbacks of the phosphorus-containing inorganic builders or the foam-producing ABS surfactants, the past has taught it is most desirable that chemicals used in large volume applications which enter the environment be biodegradable. Unfortunately, most polycarboxylic acid polymers and copolymers useful in detergent applications or as dispersants or as water treatment chemicals are not highly biodegradable.
One class of poly(carboxylic acids) believed to be biodegradable are poly(amino acids). For example, European Patent Application 454,126 A1 discloses poly(amino acids) such as poly(aspartic acid) and poly(glutamic acid) as biodegradable builders and cobuilders in detergent formulations. Poly(aspartic acid) is also disclosed as a detergent builder in U.S. Pat. No. 4,325,829 to Duggleby et al.
Poly(aspartic acid) can be formed by hydrolysis of anhydropolyaspartic acid, a.k.a. polysuccinimide. Several methods are known for obtaining polysuccinimide. Polysuccinimide can be prepared by thermal polycondensation of aspartic acid as disclosed in E. Kokufuta et al., "Temperature Effect on the Molecular Weight and the Optical Purity of Anhydropolyaspartic Acid," Bul. Chem. Soc. Japan, 61(5):1555-1556 (1978). Also, U.S. Pat. No. 5,057,597 to Koskan discloses a solid-phase process for preparing polysuccinimide by fluidizing aspartic acid with agitation in a nitrogen atmosphere at a temperature of at least 180.degree. C. for three to six hours. The resultant polysuccinimide is then hydrolyzed to form a poly(amino acid).
The hydrolysis of polysuccinimide imparts additional expense by virtue of additional raw materials and processing time. Furthermore, the hydrolysis may result in a poly(aspartic acid) solution which imparts difficulties when attempting to formulate a powdered detergent.